The present invention relates to the field of display devices, and more particularly to lighting of flat panel display devices such as liquid crystal display (LCD) devices.
LCD devices are widely used in flat panel displays for computer and display monitors, televisions, bill boards, road signs, and other applications. In some applications, for example as a computer display for notebook computers, LCD devices are desirable because they are much thinner and lighter than alternatives such as, for example, CRT (cathode ray tube) displays.
An LCD panel is generally (but not necessarily) configured as a thin rectangular panel having a first major surface (its “front”) and a second major surface (its “back”). As a rectangular panel, it has four edges, or sides, defining the boundaries of the LCD panel. The LCD panel includes a number of sub-layers such as a liquid crystal layer and a plurality of optical filter layers. An LCD screen can consist of thousands or millions of pixels covering the screen; manipulation of these pixels, in combination of a lighting subsystem, results in the displaying effect.
As is known to those skilled in the art, an LCD does not emit light; rather, the displaying effect is produce by control of light from a side or backside lighting subsystem that provides light to the LCD panel. Thus, the quality of the displayed image depends on, in part, the quality and the wavelengths of light from the lighting subsystem (typically on the backside of the LCD panel).
A common backlit LCD device includes an LCD panel with one or more fluorescent tubes running proximal to one or more edges of the LCD panel. Light pipes guide light from the fluorescent tubes or any light source to the back surface of the LCD panel. Thus, the LCD panel is backlit allowing a viewer to more easily view, from the front surface, the information on the LCD panel. Unfortunately, such edge lighting system is inefficient with up to 50% or more of the light being lost. See, for example, U.S. Pat. No. 6,672,734 B2, U.S. Pat. No. 6,768,525 B2, and U.S. Pat. No. 6,844,903 B2.
In an alternative design, an array of fluorescent tubes are placed near the back surface of the LCD panel allowing direct illumination of the back surface of the LCD panel thereby eliminating the need for the light pipes and increasing the efficiency of the lighting system. However, fluorescent light does not deliver all the primarily colors—Red, Green and Blue—which can then be combined to yield millions of secondary colors for the display. That is, the images displayed are not truly natural and brilliant as desired for some applications.
Consequently, there remains a need for an improved system for illuminating flat panel displays that overcomes or alleviates the shortcomings of the prior art devices. Semiconductor light emitting devices, such as Light Emitting Diode (LED) devices, also may be used for edge illumination of a planar array of LCD devices. For example, U.S. patent application Ser. No. 10/898,608, filed Jul. 23, 2004, entitled Reflective Optical Elements for Semiconductor Light Emitting Devices, to co-inventor Negley, and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes side emission LEDs that may be used for large area LCD and/or television backlighting.